1. Field of the Invention
The present invention relates in general to the field of electronic circuitry and, more specifically, to a system and method for providing an oscillator amplifier.
2. Description of the Related Art
Crystal oscillator amplifiers are used extensively in a wide variety of electronic circuits. As microelectronic fabrication processes advance, there is an increasing demand for oscillator amplifiers that are capable of providing accurate high-gain signal amplification, while consuming minimal power. Nominal threshold voltages in many new NMOS fabrication processes are 500 mV or less. The combination of process and temperature variation can reduce the threshold voltage, Vth, of the amplifier by more than 200 mV, meaning that a nominal Vth of 500 mV could be less than 300 mV in some cases. The DC bias voltage of a typical NMOS Pierce oscillator, which is operated in weak inversion, can therefore be 200 mV or less. As a result, such an oscillator cannot always support peak-to-peak amplitudes greater than 400 mV without clipping its output, thus creating susceptibility to noise and electromagnetic interference (EMI). It also limits the amount of hysteresis that can be designed into the buffer circuit used to convert the sinusoidal signal into a square wave.
In view of the foregoing, it is apparent that there is a need for a general purpose low power crystal oscillator circuit which maximizes signal-to-noise ratio (SNR) and which does not distort or add harmonics into the signal. In particular, there is a need for a low-power, high-gain amplifier for a crystal oscillator which can support a substantial oscillation amplitude greater than 1Vpp without clipping.
Further limitations and disadvantages of conventional processes and technologies will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.